“It is said that humans have grown weaker since we have started to eat cooked food. Shinobi no mono would normally eat unpolished, brown rice, but white rice when fighting. This is not simply becasue white rice is easier to digest but it also stems from the fact that white rice was seen as a symbol of victory.
While the martial arts contains Omote (overt; 表) techniques and Ura (covert; 裏) techniques, the Ninja diet has three sides to it: Omote, Ura, and Kū (the void; 空). The Ura technique encourages the practitioners to fill the Void with anything they can, and to eat unbalanced, strange, possibly ‘disguised’ food. Leading a deliberately irregular life also helps you to cultivate a sense of balance for different time zones (like those on shift work). When undercover, Ninja might spend long periods unable to soak up the sun, and they would therefore train to be “night owls.” Ordinary people tend to regard such unorthodox lifestyles as indicating failure, but the Ninja were in control of their own lives, and their spiritual powers of endurance helped them perfect the skills needed to transform the unconventional into commonplace activities. Whenever I travel around the world giving guidance in Ninpō Taijutsu, I never have any problems with jet lag or unusual food. Unlike many, I actually relish such experiences.
Having a healthy everyday diet is still the foundation on which one should build the kind of body which will help one’s Taijutsu grow. Above all, I recommend eating plenty of vegetables. The Ninja Kihon Happō diet consists of brown rice, tōfu, sesame, miso soup, no salt, no sugar, uncooked food, and colored vegetables. The brown rice can be roasted on a stone using sunlight. The other important thing is to eat everything, without preference or fussiness. Moreover, you should enjoy your food – and chew it well. This is useful for recovering from mental and physical fatigue.
Soldiers at war used to be fed military rations who’s three principles constituents were soya beans, brown rice, and pickled plums. Soya beans in particular are known as the “warrior’s food” or “magic food,” as they can be transformed into miso, soya sauce, and tōfu. In recent years, people all over the world have started using soya sauce and eating tōfu and brown rice, possibly becasue they have recognized this principle.”
Hatsumi, Masaaki. Way of the Ninja: Secret Techniques. (2004). pp. 109-10. ISBN 9-784770-028051